Proliferative lesions at the vitreoretinal junction zone, both those occurring spontaneously and those complicating ocular or systemic disease, are an important cause of human blindness concerning which there is little pathogenetic information. These lesions may present as subtle, sparsely cellular membranes in localized areas of the fundus, which may cause surface wrinkling retinopathy a lesion often accompanied by significant visual impairment. Less commonly these proliferative lesions may be more extensive, contain fibrous and vascular tissue, and be complicated by retinal detachment and irreversible blindness. The type of cell (or cells) comprising these membranes, their source, and the local or systemic factors that promote their proliferation remains unknown. Even less is known about the interrelationship of the minimal to the more severe and complicated lesions. In order to clearly define the cytopathologic and histopathologic features, the proposed investigation will primarily use electron microscopy to study the fine structure of varying degrees and types of proliferative vitreoretical lesions in surgically enucleated whole eye specimens. This will be supplemented with gross and microscopic studies, as well as with detailed clinical information, in order to determine the relationship of these lesions to ocular and systemic morbid processes. The information from these studies will, hopefully, contribute to a better pathogenetic understanding of proliferative vitreoretinal lesions and, thereby, to improved prophylactic and therapeutic management of affected patients.